Turbulence associated with wake vortices generated by arriving and departing aircraft pose a safety risk to other nearby aircraft, including aircraft operating on Closely Spaced Parallel Runways (CSPRs). ). Aircraft separation standards are imposed to mitigate this potential risk.. The FAA and NASA are investigating application of wind-dependent procedures for improved departure operations that safely reduce spacing restrictions to allow increased airport operating capacity. These procedures are referred to collectively as Wake Turbulence Mitigation for Departures (WTMD).

An important component of WTMD is a Wind Forecast Algorithm (WFA) being developed by MIT Lincoln Laboratory. The algorithm is designed to predict when runway crosswind conditions will remain persistently favorable to preclude transport of aircraft departure wakes into the path of aircraft on parallel runways. The algorithm has two distinct components for predicting the winds at the surface (10 m) and aloft (up to 300 m, the nominal height at which aircraft departing from parallel runways diverge and alternate forms of separation standards are applied). The surface component forecast applies a statistical approach using recent observations of winds from 1-minute ASOS observations. The winds aloft component relies on the 2 to 4 hour wind forecasts from NCEP's Rapid Update Cycle (RUC) model. The baseline version of the algorithm was developed and tested using data from St. Louis Lambert International Airport. Algorithm performance was evaluated using 1-minute ASOS observations and crosswind component measurements taken from a dedicated Light Detection and Ranging (Lidar) system.

Results of algorithm performance are presented. They show that the WFA is able to reliably predict when crosswind conditions will remain suitable for WTMD operations, with a very low error rate (approximately 10-4). Other mitigating factors within the entire WTMD system further significantly reduce the risk of a potential wake encounter to an acceptable level. The conservatism of the algorithm in avoiding false positive alerts results in a significant portion of time when actual favorable conditions are not exploited. A sensitivity analysis of algorithm parameter adjustments to increase system benefits without incurring unacceptable safety risk is also presented.

Development and demonstration of the WTMD WFA for additional candidate airports is ongoing.

This work was sponsored by the Federal Aviation Administration under Air Force Contract No. FA8721-

05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are

not necessarily endorsed by the United States Government.